JPH06226264A - Method of treating waste suspension - Google Patents

Abstract

There is disclosed a process comprising: (a) providing an aqueous suspension of particulate kaolin clay; (b) introducing into the aqueous suspension a reagent comprising a source of alkaline earth metal ions and a reagent comprising a source of carbonate ions to precipitate an alkaline earth metal carbonate in the said aqueous suspension of the said particulate kaolin clay whereby the said particulate kaolin clay present at the start of the process becomes entrained in the alkaline earth metal carbonate to form a mixed aggregated material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a by-product of hydrometallurgical refining and a wastewater of a paper mill, which has been considered to be difficult to dehydrate when dispersed in an aqueous suspension with a low solid content. The present invention generally relates to a method for treating a suspension of waste substances. Furthermore, the invention relates to the agglomerated products obtained by the above process, which have excellent properties when used in papermaking and paper coatings or as additives or fillers in paints, plastic compositions and the like.

[0002]

BACKGROUND OF THE INVENTION Many natural mineral feedstocks are subjected to particle size screening to select particles with the most suitable particle size distribution, depending on the particular application. Often, natural mineral feedstocks contain significant proportions of fine particles that are undesirable for the particular application in which the mineral feedstock is processed, and it is necessary to remove these excessively fine particles. When particle size sorting is performed on a suspension of mineral raw material in a liquid, the most common liquid is water, and undesired fine particles have a particle size of about 0.
If you have a spherical diameter equivalent to 5 μm or less,
Undesirable fine particle suspensions are often recovered in the form of dilute suspensions which are very difficult to dehydrate by conventional methods. Release of such dilute suspensions of fine mineral particles into rivers and lakes is generally unacceptable for environmental reasons. This is because the release of this undesirably very fine particle suspension is often retained in the lagoon, thus covering a large area of land that can be more beneficially used for other purposes. Is.

Organic waste composed of cellulosic fibers, in which suspended solids, such as paper mill wastewater, are generally accompanied by smaller amounts of inorganic mineral additives, is also environmentally undesirable and difficult to dehydrate. Is.

It is well known that fine particle size calcium carbonate can be chemically precipitated by contacting with a source of calcium ions and a source of carbonate ions.
The source of carbonate ions can be, for example, carbon dioxide gas in the presence of water or an alkali metal carbonate such as soda ash. TAPPI Monograph Series No.30, `` Paper Coatin
g Pigments, pp. 34-35, for the preparation of precipitated calcium carbonate, which is particularly suitable for use in the paper industry.
It describes two main industrial methods. All three methods first calcinate limestone to produce quicklime and then hydrate the quicklime in water to obtain calcium hydroxide or lime milk. In the first method, lime milk is directly carbonated with carbon dioxide gas. This method has the advantage of not forming by-products and is relatively easy to control the nature and purity of the calcium carbonate product. In the second method, lime milk is contacted with soda ash and metathesis produces a precipitate of calcium carbonate and a solution of sodium hydroxide. In order for this process to be industrially attractive, sodium hydroxide must be separated substantially completely from calcium carbonate. In the third major industrial method, lime milk is first contacted with ammonium chloride to produce calcium chloride solution and ammonia gas. The calcium chloride solution is then contacted with soda ash and metathesis produces a solution of precipitated calcium carbonate and sodium chloride.

US Pat. No. 5,082,887 describes a method of treating an aqueous suspension of fine mineral particles with a polymer containing high molecular weight carboxy groups to agglomerate the particles. An excess of calcium ions is then added and the calcium salt of the polymer containing carboxy groups is precipitated in situ on the mineral flocs to form agglomerates of mineral particles. Gaseous carbon dioxide is then added to this slurry and reacted with the residual calcium ions in the slurry to precipitate calcium carbonate on the polymeric carboxy calcium salt.

US Pat. No. 3,152,001 first precipitates calcium carbonate from an aqueous solution and then modifies the surface of the precipitated calcium carbonate with SiO ₂ .
The method of manufacturing the additive is described. After that, the finely divided silicate is precipitated on SiO ₂ -modified calcium carbonate. The obtained additive is used as an additive for reinforcing the elastomer.

US Pat. No. 2,470,577 describes additive materials prepared by the simultaneous precipitation of calcium carbonate and calcium silicate from conventional reaction solutions.

[0008]

SUMMARY OF THE INVENTION The present invention is a method of treating an aqueous suspension of particulate matter comprising the step of precipitating an alkaline earth metal carbonate in the aqueous suspension of particulate matter. , Whereby the particulate matter present at the beginning of the process is collected in an alkaline earth metal carbonate precipitate. The method of the invention is in particular an industrial by-product,
It is suitable for treating finely divided particulate matter, which is usually difficult to recover by dehydration. The resulting products are useful as additives or dyes, respectively, for use in papermaking or paper coating.

[0009]

SUMMARY OF THE INVENTION In a first aspect of the invention, there is provided a method of treating an aqueous suspension of particulate waste material. The method comprises the step of precipitating an alkaline earth metal carbonate in an aqueous suspension of the particulate matter, whereby the particulate matter present at the beginning of the step is alkaline earth metal. Collected in the metal carbonate precipitate.

The particulate waste material preferably contains a certain proportion of particulate inorganic material. The particulate inorganic mineral (if present) is preferably finely divided. Finely divided means that the particulate inorganic minerals generally have an average particle diameter of less than 1 μm and usually less than about 0.5 μm.

Alternatively or in addition to the above, the particulate waste material is an organic waste component, eg, typically 7
Waste organic fibers (eg cellulosic fibers) having a length not exceeding 5 μm may be contained.

The aqueous suspension is preferably dilute.
Dilute means that the aqueous suspension contains, on a dry weight basis, no more than about 20% by weight of dry particulate matter, more preferably 10% by weight or less of the aqueous suspension. means. If the waste suspension to be treated is a paper mill effluent, its solids content is preferably significantly lower than 10%, for example of the order of 1%.

The present invention is directed to finely divided kandite clay minerals such as kaolin, bentonite, montmorillonite, saponite, hectorite or beidellite (b).
eidite) smectite clay, paper mill wastewater (usually a mixture of cellulosic fibers and inorganic additives)
It is particularly suitable for agglomeration of particulate matter that is an industrial by-product such as. The present invention is also suitable for treating soft mud produced as a by-product of beneficiation of phosphate ores such as apatite, or as a by-product of diamond extraction from kimberlite-type clay minerals. Such ore-enriched soft mud contains inorganic components and, optionally, organic components. The particulate matter is finely divided, eg, smaller than 1 μm, and typically about 0.5 μm.
These substances are very difficult to dehydrate when they are industrial by-products of this type having an average particle size smaller than m and when present as an aqueous suspension containing not more than about 10% by weight of dry by-products. The invention is particularly advantageous.
The aqueous suspension of agglomerated product obtained by the method of the present invention is relatively easy to dehydrate.

The method of the present invention may also be used to treat organic waste suspensions that would otherwise be difficult to dehydrate. Then, coaggregation with the precipitated alkaline earth metal carbonate results in a useful product.

The particles of particulate material may have on their surface a polymeric material such as a dispersant added in the preceding separation step. This has the effect of making dehydration of the suspension of particulate matter more difficult and therefore the present invention is more advantageous.

The alkaline earth metal carbonate is most preferably calcium carbonate.

In the method of the present invention, an alkaline earth metal carbonate precipitate is formed by introducing a source of alkaline earth metal ions and a source of carbonate ions into a suspension of particulate minerals. Can be done. As a result, the desired alkaline earth metal carbonate precipitate can be formed in situ , and the particulate minerals can be collected. The first reagent added is preferably
It should be evenly distributed throughout the aqueous suspension of particulate matter to prevent the formation of local concentration gradients. Thorough mixing is desirable when the first reagent is poorly soluble, as is the case with calcium hydroxide. To ensure a uniform distribution of the precipitate,
It is also desirable to stir the suspension while adding the second reagent.

It is desirable to add the carbonate ion source after adding the alkaline earth metal ion source. If the alkaline earth metal is calcium,
Precipitation of the calcium carbonate in the scalenohedron form is guaranteed, giving the agglomerated product the best light scattering properties when used in papermaking or paper coatings.

The source of alkaline earth metal ions is preferably an alkaline earth metal hydroxide (known as lime milk when the alkaline earth metal is calcium). Alternatively, it may be, for example, a water-soluble alkaline earth metal salt such as chloride or nitrate. The alkaline earth metal hydroxide may be added to the previously prepared aqueous suspension, or in the suspension an alkaline earth metal oxide (eg if an aqueous suspension of calcium hydroxide is desired). Can be prepared in situ by quenching lime.

The source of carbonate ions is preferably carbon dioxide gas introduced into the suspension containing the particulate matter and the source of alkaline earth metal ions. The carbon dioxide gas may be substantially pure as supplied by a gas cylinder, or it may be present in a mixture of gases such as flue gas. Alternatively, the source of carbonate ions can be an alkali metal carbonate or ammonium carbonate. Sodium carbonate is particularly preferred in view of its relative price and availability.

When the process according to the invention is used for the treatment of suspensions of organic wastes, for example for the treatment of wastewater from paper mills whose suspended solids consist mainly of cellulosic fibers, alkaline earths The source of metal ions is either, for example, by the addition of alkaline earth metal oxides such as calcium oxide or quicklime, or by the addition of alkaline earth metal hydroxides prepared separately in suspension, It can be introduced in suspension.

Whether the alkaline earth metal oxides are solubilized in either waste water or fresh water, the water temperature can be room temperature, heating to a temperature in the range of 40 ° C to 50 ° C. The suspension of alkaline earth metal oxides in water is preferably and vigorously stirred, preferably for a time of up to 30 minutes, ensuring that the dissolution is complete.

The amount of alkaline earth metal ion source and carbonate ion source used is sufficient for precipitation of the alkaline earth metal carbonate, and the dry solids content of the aqueous suspension is increased from 10% to 20% by weight. Increasing amounts are preferred. The weight ratio of fine mineral to alkaline earth metal carbonate (preferably calcium carbonate) depends on the nature of the fine mineral. In order to obtain sufficient dehydration, for example bentonite, at least 80% by weight of the mixture must be alkaline earth metal carbonate, whereas in the case of fine kaolinite only about 25% of the mixture is alkaline earth metal carbonate. Any metal carbonate may be used.

A suspension of alkaline earth metal carbonate (preferably calcium carbonate) and a suspension containing the collected particulate matter (eg industrial by-products) in relatively diluted form in papermaking. It may be added directly to the composition to provide additive particles of papermaking fibers. Alternatively, the suspension may be dehydrated by any conventional method, such as pressure filtration or centrifugation.

If desired, reducing bleaching agents may be added to the suspension containing particulate matter or by-products to improve whiteness. Reducing bleaching agents are, for example, sodium dithionite, or dithionite salts such as zinc dithionite,
Alternatively, it can be zinc powder and sulfur dioxide. The amount of reducing bleach used is preferably in the range of 1.5 to 7.5 grams of reducing bleach per kilogram of dry particulate material. The bleaching agent can be added after the addition of the first reagent and before the addition of the second reagent.

The suspension of the alkaline earth metal carbonate precipitate and the collected particulate matter is much easier to dewater than the original suspension consisting only of particulate matter. Because, when a cake of mixed solid material is formed by filtration or centrifugation, the dense state of the particles is such that the cake has much higher water permeability than the cake of the particulate matter by-product alone. Because it is in. Also, the mixed solid materials provide advantageous light scattering properties when used as a paper additive or a paper coating pigment.

In a second aspect of the invention, the precipitated alkaline earth carbonate (preferably calcium carbonate) and the particulate matter collected in the alkaline earth metal carbonate precipitate are substantially There is provided a mineral pigment / additive composite comprising an aggregate comprising: Such agglomerates can be used in the preparation of papermaking or paper coating compositions. The papermaking composition comprises cellulosic fibers and other conventional additives known in the art in aqueous suspension, in addition to the aggregated additives of the present invention (and any other additive materials). A typical papermaking composition contains up to about 67% by weight dry additive material, based on the dry weight of the papermaking fibers, and also 0.1 to 2 based on the dry weight of the additive material. Cationic or anionic retention aids may be included in amounts ranging from weight percent. The papermaking composition may also include a sizing agent, which may be, for example, a long chain alkyl ketene dimer, wax emulsion or succinic acid derivative. The composition may also include dyes and / or optical brighteners. The paper coating composition comprises an adhesive in an aqueous suspension in addition to the agglomerated pigments of the invention (and any other additive material). The formulation of the paper coating composition depends on the purpose for which the coated paper is used, ie offset or gravure printing. Generally, the amount of adhesive ranges from 3 to 35% by weight of adhesive solids, based on the dry weight of the coating pigment. There may also be present from 0.01 to 0.5% by weight of dispersant, based on the dry weight of the coating pigment. Usually enough alkali is added to raise the pH to about 8-9. The adhesive solid content is water-dispersible synthetic resin or latex such as starch, styrene-butadiene copolymer, polyvinyl alcohol, acrylic polymer, polyvinyl acetate, butadiene-acrylonitrile copolymer, methyl cellulose, sodium salt of carboxymethyl cellulose or cellulose derivative such as hydroxyethyl cellulose. Alternatively, it may be a proteinaceous substance such as casein, animal glue or vegetable protein.

[0028]

The present invention will be described based on the following examples.

Example 1 Quicklime (252 g) was added to 50
At a temperature of 0 ° C., 4,500 cm ^{3 of} an aqueous suspension containing 7.5% by weight of kaolin clay particles with an average particle size of 0.22 μm were added. This suspension was stirred vigorously for 25 minutes to ensure sufficient slaked lime. The pH of the suspension is 12.
It was 5.

A gas mixture containing 25% by volume of carbon dioxide was then introduced into the suspension of clay particles and calcium hydroxide at a flow rate of 5,242 cm ³ / min. This flow rate corresponds to 0.013 mol per 1 minute per 1 mol of calcium hydroxide. The gas mixture was introduced into the suspension as a fine stream of bubbles and vigorous stirring was maintained during the introduction.

The pH of the suspension was continuously monitored and the introduction of the gas mixture was continued until the pH of the suspension dropped below 8.0.

The particulate constituents of the resulting suspension containing 54% by weight of calcium carbonate were examined by electron microscopy and the results were:
It was found to consist of co-aggregated mixed minerals. Figure 1
Is an electron micrograph of the particulate component of the resulting suspension,
The tabular particles are kaolinite, and white "fluffy"
The particles are precipitated calcium carbonate.

Example 2 In each case, different amounts of the mixed minerals produced were added to the above suspension of kaolin clay particles, such that the calcium carbonate varied from 35% to 73% by weight. Was added and the experiment described in Example 1 was repeated several times. 4,5 without kaolin particles
Another suspension was prepared by soaking 252 g of quicklime in 00 cm ³ of water and served as a control. In each case, 0.013 mol of carbon dioxide per mol of calcium hydroxide was introduced into the suspension per minute.

The mixed mineral suspension produced in each case is filtered, and the mixed mineral cake is remixed with water to form a suspension containing 30% by weight of dry mixed minerals. The Kubelka-Munk scattering coefficient S was measured by the following method: Arjo Wiggins Apple under the registered trademark "SYNTEAPE".
A sheet of synthetic plastics paper material sold by ton plc is cut into many pieces, each measuring 10 cm x 6 cm, and each piece is weighed and the "ELRE
With the "PHO" spectrophotometer, you can try the percentage of reflectance for light of wavelength 457nm when placed on a black background,
The background reflectance R _b was obtained. The weighed pieces of plastic paper were then coated with different amounts of a suspension of mixed minerals and coated with a weight in the range of 5 to 20 gm ^-2 . Dry each coating in air,
Then place the area of dry coating on each piece of plastic paper, place the circular template on the coating,
The excess coating outside the perimeter of the template was then carefully removed and normalized. The weight of each piece of plastic paper with coated areas was then re-weighed and the coating density X (kg · m ⁻² ) was calculated from the weight difference and the area of the coated area.

Each coated area was then placed on (a) a piece of plastic paper placed on a black background (R ₀ ) and (b) on a piece of laminated uncoated plastic paper. In the case (R ₁ ), the reflectance for light having a wavelength of 457 nm was tried. Finally, 457nm
The reflectivity for light of wavelength was measured on the stack of uncoated pieces (r).

From these measurements, the reflectance R _c of the coating alone was calculated from the following equation:

[0037]

[Equation 1]

Then, the transmittance T _{c of the} coating was calculated from the following equation.

[0039]

[Equation 2]

From these two quantities, it is possible to calculate the theoretical value of the reflectance R ₀₀ of an infinitely thick coating layer of the same substance from the following equation:

[0041]

[Equation 3]

The Kubelka-Munk scattering coefficient S, expressed in m ² · Kg ⁻¹ , can be calculated from the following equation:

[0043]

[Equation 4]

However,

[0045]

[Equation 5]

And

[0047]

[Equation 6]

It is

This scattering coefficient S is plotted against the coating density X, and in each case 8 g · m ⁻²
The value which became the coating density at was calculated by interpolation.

The results obtained are shown in Table 1 below.

[0051]

[Table 1]

Example 3 Described in Example 1 except that 1.69 g of sodium dithionite as a reducing bleach was added to the suspension of kaolin clay particles prior to the addition of quicklime. The same experiment was repeated. The particulate component of the suspension, which had been treated with carbon dioxide gas, was separated by filtration and dried in an oven at a temperature of 80 ° C. for 16 hours. The dry cake obtained is pulverized and
LREPHO ”spectrophotometer at 457 nm and 5
The reflectance for light having a wavelength of 70 nm was measured.

The above experiment was repeated except that no sodium dithionite was added to the suspension of kaolin clay particles.

The results obtained are shown in Table 2 below.

[0055]

[Table 2]

Example 4 In each case different amounts of quicklime were added to kaolin so that the composition of the mixed minerals produced varied in the range 0.5% to 99.5% by weight of calcium carbonate. It was added to a suspension of clay particles and the experiment described in Example 1 was repeated several times. In each case, per minute,
0.013 mol of carbon dioxide was introduced into the suspension per mol of calcium hydroxide.

A small sample of the mixed mineral suspension produced in each case was poured into a Buchner filter funnel equipped with a piece of standard filter paper. The side tube of the suction bottle was connected to a vacuum source, and suction filtration was performed. The filtrate was collected in a graduated cylinder placed inside a suction bottle, and the volume of the collected filtrate and the time elapsed from the start of filtration were recorded at regular time intervals. The square root of the recovered volume was plotted in the figure against the elapsed time, and a curve having a large linear portion in the center was obtained. For each case,
The slope of this straight line was recorded.

The relationship between the square root of the volume of the collected filtrate and the elapsed time is expressed by the Carmen-Kozeny equation.

[0059]

[Equation 7]

However, Q is the amount of the recovered filtrate; T is the elapsed filtration time; A is the area of the filtration medium; P is the pressure difference applied to the filtration medium; E is the porosity in the filtration cake; v
Is the viscosity of the suspending solvent; S is the specific surface area of the particulate phase; and d is the density of the particulate phase.

The slope Q ² / T of the straight line portion of the graph plotted for each suspension gives an index of the filtration rate in each case,
And under this experimental condition, A, P, v, S and d
As can be assumed to be constant, it can be seen that the standardized filtration rate F is given by

[0062]

[Equation 8]

However:

[0064]

[Equation 9]

However, W _c is a part by weight of water in the cake; S _c
The parts by weight of the individuals in the cake; W _s is the weight of water in the suspension; and S _s is the weight of the individuals in the suspension; a.

Precipitated calcium carbonate prepared from a kaolin clay suspension by independently carbonated lime milk was mixed in different amounts with a suspension of 4,500 cm ³ of fine kaolin clay particles, Multiple suspensions were prepared. The filtration rate of each mixed suspension and the weight percentage of dry matter in the cake were measured as above.

The results obtained are shown in Table 3 below.

[0068]

[Table 3]

These results show the following.
If the weight percentage of precipitated calcium carbonate in the mixture is the same, the precipitation of calcium carbonate in the presence of fine kaolin results in independent precipitation of calcium carbonate,
Thereafter, a higher filtration rate is obtained than when added to a fine suspension of kaolin.

EXAMPLE 5 Different amounts of quicklime were added to an aqueous suspension of 4,500 cm ³ containing 7.5% by weight of Wyoming sodium bentonite having an average particle size of less than 0.1 μm at a temperature of 50 ° C. Was added. In each case, the suspension was stirred vigorously for 25 minutes to ensure a sufficient slaked lime.

Next, 1 part of calcium hydroxide was added per minute to each of the suspensions of bentonite particles and calcium hydroxide.
With carbon dioxide at a rate of 0.013 mol per mol, 2
A gas mixture containing 5% by volume of carbon dioxide was introduced. The gas mixture was introduced into the suspension as a fine bubble stream, with vigorous stirring during the introduction. The pH of the suspension was continuously monitored and the introduction of the gas mixture was continued until the pH of the suspension dropped below 8.0.

The filtration rate F, and the weight percentage of water retained on the filter cake, were determined for each suspension as described in Example 4 above. The results obtained are shown in Table 4 below.

[0073]

[Table 4]

These results show the following.
If the amount of calcium carbonate precipitated in the suspension is greater than about 90% of the total weight of dry bentonite and calcium carbonate, the suspension can be dehydrated by very fast filtration. However, even if the proportion of calcium carbonate in the mixture is 80% by weight, the filtration rate is acceptable in an industrial way.

Example 6 80% by weight has a particle size distribution consisting of particles having an equivalent spherical diameter of less than 2 μm,
To 1000 ml of an aqueous suspension containing 180 g of kaolin clay was added 11.25 g of quicklime. The solids content of this kaolin clay suspension before addition of quicklime was 16.2% by weight
Met. The suspension was kept at a temperature of 50 ° C. and stirred vigorously for 25 minutes to ensure sufficient soaking of the quicklime.

A gas mixture containing 25% by volume of carbon dioxide was then introduced into the suspension as a fine bubbling stream at a carbon dioxide rate of 0.13 mol / mol calcium hydroxide / min. . The temperature of this suspension was kept at 45 ° C. and the gas mixture was introduced with continuous stirring of the suspension until the pH of the suspension was below 8.0.

11.2 in 1000 ml of an aqueous suspension containing 60 g, 20 g and 6.7 g of kaolin clay, respectively.
The same experiment as above was repeated three more times, except that 5 g of quicklime was added. In each case, the solids content of the suspension of kaolin clay before the addition of quicklime was 16.2%, 5.8%, 2.0% and 0.7% by weight, respectively.

In 1000 ml, only 1 kaolin clay was added.
A suspension containing 80 g was also prepared. Quicklime was added to 1000 ml of water and another suspension of the formed calcium hydroxide carbonated under the above conditions was further prepared.

The filtration rate F, and the weight percentage of water retained on the filter cake, were determined for each suspension as described in Example 4 above. The results obtained are shown in Table 5 below.

[0080]

[Table 5]

Example 7 A sample of wastewater from a paper mill contained 0.27% by weight suspended solids, mainly cellulosic fibers and less inorganic additive particles than the fibers. 14g each for 3 liters of this wastewater,
28g and 56g quicklime were added. This mixture of wastewater and quicklime was stirred vigorously at a temperature of 45 ° C. to complete the quicklime slakement.

In 75 minutes, at a rate calculated to complete the conversion of all calcium hydroxide present to calcium carbonate, 25% by volume of carbon dioxide, the balance being air, was added to each suspension. Introduced. In each case, the temperature of the suspension was kept at 45 ° C. during carbonation.

Each sample of suspension was filtered and the filtration rate was determined by the method described in Example 4. As a comparison, the filtration rate of a sample of untreated wastewater was also investigated. The results obtained are shown in Table 6 below.

[0084]

[Table 6]

Each of the three products containing precipitated calcium carbonate was examined by scanning electron microscopy and found to be present in fine scalenohedron-like precipitated calcium carbonate particles and originally in the wastewater. It was found to consist of fibers.

Example 8 Another sample of wastewater from a paper mill was weighed and filtered, and the filter cake was dried at 110 ° C. The solids content of this wastewater was 0.3% by weight. The dried residue was heated in an oven at 1000 ° C. for 1 hour and the residue heated at high temperature was weighed again. The weight loss on heating of the dry residue was 89%, which is believed to be mainly due to the cellulose fiber content in the dry residue. It is known that the inorganic additive used in the papermaking process in wastewater producing paper mills consists mainly of calcium carbonate, so the high temperature heating residue corresponding to 11 wt% dry residue is calcium oxide. it is conceivable that. 11% by weight of calcium oxide corresponded to 19.6% by weight of calcium carbonate, so that the approximate composition of the solid components of the wastewater was 8%.
It is estimated that 0% by weight is cellulose fibers and 20% by weight is calcium carbonate.

A suspension of calcium hydroxide was prepared by soaking 112 g of quicklime in 1 liter of water at a temperature of 50 ° C. with vigorous stirring for 25 minutes. Assuming that the quicklime is completely dissolved, the suspension thus prepared will contain 148 g of calcium hydroxide per liter.

After carbonated with a gas containing carbon dioxide, an amount of each calcium hydroxide suspension calculated to contain 60%, 80% and 90% by weight of precipitated calcium carbonate, respectively, L was added to 3 independent wastewaters. The gas is 25% by volume carbon dioxide with the balance air. This gas was introduced into the mixture of calcium hydroxide suspension and wastewater at such a rate that precipitation was completed in 5 minutes.

Each of the three treated wastewaters was filtered and the filtration rate was determined by the method described in Example 4. For comparison, the filtration rate was also investigated on untreated wastewater samples. The results are shown in Table 7 below.

[0090]

[Table 7]

According to the present invention, it can be seen that when calcium carbonate is precipitated in wastewater, the filtration rate of wastewater is greatly increased.

90% by weight, obtained by filtering the wastewater
The filter cake, in which the solid components of, consisted of precipitated calcium carbonate, was dried, pulverized, and the resulting pulverulent material was used as an additive in a papermaking composition. Paper handsheets filled with the composite material prepared as described above were prepared by the following method. Soaking 400 g of bleached spruce sulfite pulp in 10 liters of filtered water for 4 hours,
The mixture was then milled for 10 minutes in a turbine mixer with rotating blades rotating at a speed of 1500 rpm. The contents of the mixer were washed with another 10 liters of water and transferred to a laboratory beater. An additional 2 liters of water was added to the beater and the mixture was milled for 16.5 minutes. At this stage the stock contained about 1.8% by weight dry pulp. Canadian Standard Freeness 3
The time to mill the mixture was selected to give an optimum compromise to the brightness and strength properties of the stock, corresponding to 00. Next, water was added to 800 ml of stock to make 2 liters, and the mixture was pulverized by a laboratory disintegrator having a rotary vane operating at 15,000 revolutions. Filtered water was added to bring the stock volume to 4 liters and the dried and textured sheet was weighed by pouring it over a suitable wire screen to form a paper sheet from a small sample and checked for density. Add water if needed,
A dry pulp density of 0.3% by weight was used.

The papermaking stock formed as described above was divided into three parts, and different amounts of the granulated composite additive were added to each stock and stirred by hand.

Handsheets were prepared from each of the three paper stocks containing the additive according to the procedure described in TAPPI Standard No. T205 om-88, "Formation of Handsheets for Physical Testing of Pulp". 4 for each handsheet
00 ml of stock was poured into a sheet former to remove excess water.

The ash or inorganic content of the paper formed from each of the three stocks was determined by baking a sample of the paper formed from the stock according to the procedure described in TAPPI Standard No. T413 om-85. It was

Of paper formed from each of the three stocks,
The brightness or the reflection percentage for the purple light was measured as No. DATACOLOR 2000 equipped with 8 filters (wavelength of 457 nm)
It was measured by a brightness meter.

The opacity of each of the paper samples was determined by
Measured with a DATACOLOR 2000 luminance meter equipped with 10 filters (green filter covering a broad spectrum of wavelengths). Measuring the percentage of incident light reflected
Performed with a stack of 10 sheets deposited on top of the black cavity ( _Roo ). The 10 sheets were then replaced by the top sheet in the stack and another measurement of percent reflection was made on the black cavity (R). The opacity percentage was calculated by the following formula.

Percent Opacity = 100 × R / R _oo This procedure was performed a total of 10 times. Each time, a different paper was placed on top of the sheet stack and the average percent opacity was examined.

The procedure described in Example 2 was repeated except that in each case a paper sample prepared by the above method was used in place of the coated synthetic plastic paper material described in Example 2. In each of the samples, kubelka-
The Munk scattering coefficient S was investigated. No. The measurement was carried out using a DATACOLOR 2000 luminance meter equipped with 8 filters.

Handsheets from each batch should include TAPPI St
The burst strength was tested by the test described in andard No. T403 om-85. Burst intensity is 30.5 in diameter
mm through a rubber tire flam on a circular area of paper,
It is defined as the hydrostatic pressure in kilopascals required to cause a substance to burst when the pressure is increased at a controlled constant rate. The tested area of the material is initially flat and held fixed at the periphery, but expansion during the test is acceptable. Each sample of the sheet was also dry-weighed and the weight of the dry sample was used to express the weight per unit area in g / cm ² . The burst ratio was obtained by dividing the weight burst strength per unit area of paper.

For comparison, as a papermaking composition additive, trade name "CALOPAKE F", John &
E. The above experiment was repeated using a proprietary product of precipitated calcium carbonate manufactured by Sturge. The particle size distribution of this material is such that the diameter of particles with a median weight is 3.0μ.
The distribution is such that m. The amount of this proprietary additive used in each of the three papermaking stocks was as close as possible to the same amount as the composite additive used in the three stocks of the inventive experiment above.

As a further comparison, handsheets were prepared from additive-free papermaking stock and tested as described above.

The results are shown in Table 8 below.

[0104]

[Table 8]

The brightness of the added paper obtained with the composite additive material of the present application is slightly inferior to that of the proprietary precipitated calcium carbonate, but both the opacity and the scattering coefficient are of the composite additive material of the present application. It will be appreciated that the case is better and the burst intensities are about the same.
The brightness of the composite additive is as described in Example 3 above.
It can be improved by the use of reducing bleaches.

[Brief description of drawings]

FIG. 1 is an electron micrograph of a particulate component of a suspension containing co-agglomerated mixed minerals obtained in Example 1.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location D21H 19/38 17/67 // B01D 21/01 102 7824-4D

Claims (16)

[Claims] 1. A method of treating an aqueous suspension of particulate waste material, comprising the step of precipitating an alkaline earth metal carbonate in the aqueous suspension of particulate material, whereby
A method of collecting the particulate matter present at the beginning of the step in an alkaline earth metal carbonate precipitate. 2. The method of claim 1, wherein the particulate waste material contains a proportion of particulate inorganic material. 3. The method of claim 2, wherein the particulate inorganic material has an average particle diameter of less than about 1 μm. 4. The method of claim 3, wherein the particulate inorganic material has an average particle diameter of less than about 0.5 μm. 5. The method according to claim 1, wherein the particulate waste material contains an organic waste component. 6. The method of claim 5, wherein the organic waste component comprises waste organic fibers having a length of less than 75 μm. 7. The aqueous suspension is about 2 on a dry weight basis.
Less than 0% by weight, preferably 10% by weight on a dry weight basis
7. The method of any of claims 1-6, containing less than dry particulate matter. 8. The method according to claim 1, wherein the particulate material is an industrial by-product selected from the following group: finely divided kandite clay mineral, such as kaolin, Produced as a by-product of the beneficiation of bentonites, montmorillonites, saponites, smectite clay minerals such as hectorite or beidellite, paper mill effluents, and beneficiation of phosphate ores like apatite or the extraction of diamonds from kimberlite-type clay minerals. Soft mud. 9. The method according to claim 1, wherein the alkaline earth metal carbonate is calcium carbonate. 10. The alkaline earth metal carbonate precipitate is formed by introducing a source of alkaline earth metal ions and a source of carbonate ions into the suspension of particulate minerals. The method according to any one of claims 1 to 9. 11. The method of claim 10, wherein the source of alkaline earth metal ions is selected from alkaline earth metal hydroxides and water soluble salts of alkaline earth metals. 12. The method according to claim 10 or 11, wherein the carbonate ion source is carbon dioxide gas, alkali metal carbonate, or ammonium carbonate. 13. A dry solid of an aqueous suspension, wherein the amounts of the alkaline earth metal ion source and carbonate ion source used are sufficient to precipitate the alkaline earth metal carbonate. 13. The method according to claim 10, 11 or 12, wherein the content is increased to within the range of 10% to 20% by weight. 14. A mineral pigment / addition containing a precipitated alkaline earth carbonate and an agglomerate consisting essentially of particulate matter collected in the alkaline earth metal carbonate precipitate. Agent complex. 15. An aqueous suspension of the agglomerated additive according to claim 14 or the agglomerated additive prepared according to any one of claims 1 to 13 and a cellulosic fiber. A papermaking composition contained in a liquid. 16. An agglomerated pigment according to claim 14,
Alternatively, a paper coating composition containing, in an aqueous suspension, an aggregated pigment prepared as described in any one of claims 1 to 13 and an adhesive.